config_service: change error message for error 403.

appengine/config_service/ui/common/auth-signin.html

 <!--
   Copyright 2017 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
 
   The `auth-signin` element displays sign-in/sign-out button, user email and
   avatar.
   It has a google-signin/google-signin-aware element under the hood that handles
   the actual OAuth logic.
 
@@ skipping 73 matching lines @@
           observer: '_makeHeader'
         },
 
         client_id: {
           type: String
         },
 
         initialized: {
           type: Boolean,
           value: false,
+          notify: true,
           observer: '_onInitialized'
         },
 
         profile: {
           type: Object,
           notify: true
         },
 
         signed_in: {
           type: Boolean,
@@ skipping 64 matching lines @@
         this.$.aware.signIn();
       },
 
       signOut: function() {
         this.$.aware.signOut();
         window.location.reload();
       }
     });
   </script>
 </dom-module>